Manufacturing process for ring-shaped parts

ABSTRACT

The present invention relates to a manufacturing process for ring-shaped parts having high wear resistance and mechanical strength. Raw material powder containing (weight %) C at 0.4-0.9%, Ni at 1.5-4.0%, Mo 0.2-0.6%, and a remainder consisting of Fe and unavoidable impurities, is compacted and shaped, thereafter sintered and forged; obtained sintered body is hardened by heating at a temperature within a range of 800°-950° C., thereafter high temperature tempering is carried out for 20-60 minutes at a temperature within a range of 570°-700° C.; then the surface layer of the inner periphery and/or outer periphery of said sintering body is heated; then if required, low temperature tempering (temper process) is carried out at a temperature within a range of 160°-220° C., and whereby the hardness of the surface layer, for which abrasive resistance is required, reaches a value of HRC 58-63 degree, and the hardness of the middle layer falls within a range of HRC 25-40 degree.

FIELD OF THE INVENTION

The present invention relates to a manufacturing process for ring-shapedparts, which is suitable for the production of all kinds of ring-shapedmachine parts which have sliding face of irregular shape at the inner orouter surface thereof, such as a sprocket, a pulley, a race of a one-wayclutch, which is one component forming the auto-transmission of a car, acam, etc.

PRIOR ART

In general, when manufacturing the aforementioned types of ring-shapedparts by powder sintering, a method wherein the raw material powder isfirst compacted and then sintered and is subsequently forged into apredetermined shape and sintered for a second time; the resultingsintered body then undergoes machine processing such as cutting andgrinding, and is shaped into a predetermined ring shape; high frequencyhardening is then carried out for the inner or outer surfaces of thering-shaped part in order to increase the hardness of the aforementionedsurface and improve the abrasion resistance, then the hardened bodyundergoes tempering at a relatively low temperature (at approximately180° C. for 30 min.), a so-called "temper process".

However, although it is possible in the aforementioned manufacturingprocess for ring-shaped parts to obtain a predetermined hardness at theinner and outer periphery by high frequency hardening, the degree ofhardness at the middle layer of the aforementioned parts in particularbecomes too high; a moderate hardness (in other words, a greattoughness) is difficult to obtain, and therefore there is a disadvantagein that it is difficult to manufacture machine parts with high radialcrushing strength constant which have came into demand in recent years.

For this reason, one may think of a manufacturing process for increasingthe hardness of the aforementioned surfaces, in which, in contrast tothe aforementioned powder sintering method, a prototype is firstproduced by previous forging, and after various machine processes havebeen performed thereon and a predetermined shape of the aforementionedring-shaped part is obtained, high frequency hardening is performed atthe inner peripheral layer or outer peripheral layer which has to behardened, as necessary.

However, in the aforementioned manufacturing process through forging,there is in particular the problem that if the inner or outer peripherallayers are of irregular shape, a great amount of labor is required inall the machine processes in order to produce the aforementioned shapedparts, causing a complication of the process and increasing the cost ofmanufacturing.

DISCLOSURE OF THE INVENTION

Here, the inventors decided to utilize the powder sintering techniquesused in the production of general machinery parts, and carried outenergetic research with the purpose of manufacturing ring-shapedmechanical parts having radial crushing strength constants not inferiorto those made by forging. As a result the following manufacturingprocess was discovered. In the process, sintering and forging werecarried out after compacting of a raw powder material which is composedof a composition containing (weight %) C at 0.4-0.9%, Ni at 1.5-4.0%, Moat 0.2-0.6%, and a remainder consisting of Fe and unavoidableimpurities. A sintered body superior with respect to its utilization asa mechanical part was obtained by using the abovementioned raw powdermaterial. After hardening the obtained sintered body at a temperaturewithin the range of 800°-950° C., high temperature tempering at atemperature within the range of 570°-700° C. for 20-60 minutes iscarried out. Then the surface layer of the inner and/or outer periphery,which requires a high degree of hardness, of said sintered body ishardened. By this method we can obtain ring-shaped parts which have ahigh radial crushing strength constant for the entire body, because themiddle layer has a desirable hardness in a rang of HRC 25-40, and a highhardness which is required for the inner and/or outer peripheral surfaceis obtained. By carrying out low temperature tempering (temper process)within the range of 160°-220° C. on the obtained product, it is possibleto improve the radial crushing strength constant even further.

The present invention is based on this idea; even when the shape iscomplicated, manufacturing is easy, and the required hardness at thesurface layer of inner and outer peripheries, which are sliding parts,can be attained, and furthermore it is an object of the presentinvention to offer a manufacturing process for ring-shaped parts whichhave a high radial crushing strength constant for the entire part body.

Hereinafter, the reasons for limiting the component composition of theFe-sintered raw material in the present invention, in the above statedway, are explained.

(1) C

The C component is used in the Fe-sintered raw material for increasingthe strength thereof; however, the material becomes a hyper-eutectoid ifthe amount contained exceeds 0.9 weight %, which results in a decreasein abrasion resistance and strength due to the coarseness of thehardening structure; and if, in contrast, this contained amount is lessthan 0.4 weight %, sufficient strength in the middle layer is notattained, the radial crushing strength constant decreases and apredetermined hardness by hardening (such as high frequency hardening)in order to attain the appropriate surface hardness cannot be obtained.Therefore, the aforementioned proportion of C is determined to liewithin the range of 0.4-0.9 weight %.

(2) Ni

The Ni component, which is an alloying element of a substitutional solidsolution for Fe, is added if toughness is required; however, if thecontained amount exceeds 4.0 weight %, a further increase of this effectcannot be expected, and since it is an expensive alloying element, thisis not economical either. On the other hand, if the contained amount isless than 1.5 weight %, a sufficient toughness can not be obtained, andas a result, there is the inconvenience of a decrease in the strength ofthe part. For these reasons, the aforementioned contained amount of Niis determined to lie within the range of 1.5-4.0 weight %.

(3) Mo

The Mo component is added to increase the ability to be hardened;however, if the contained amount exceeds 0.6 weight %, exteusibilitydecreases and fragility against shock occurs. On the other hand, if thiscontained amount is below 0.2 weight %, hardenability decreases andthere occurs non-uniformity in the hardness. Therefore, theaforementioned contained amount of Mo is determined to lie within therange of 0.2-0.6 weight %.

Next, after sintering and hardening, high temperature tempering iscarried out for 20- 60 minutes in a temperature range of 570°-700° C.;for obtaining a high mechanical strength in the whole mechanical partwhich constitutes a component in the product, and for attaining an HRC24-40 of moderate hardness at the middle layer of the aforementionedpart; and if the aforementioned tempering temperature exceeds 700° C.,the middle layer becomes too soft and a sufficient work strength is notattained; and if on the other hand the temperature does not reach 570°C., there is the inconvenience that the hardness of aforementionedmiddle layer becomes too high and inferior in toughness, and therebyconversely becomes fragile.

Next, it is desirable that the hardening of the surface layer of theaforementioned sintered body is performed by high frequency hardeningwithin a temperature range of 800°-950° C. Using high frequencyhardening, it is possible to harden only the surface layers within adepth-range of 1-2 mm required for most mechanical parts, to HRC 58-63required for the mechanical sliding portion. However, if theaforementioned temperature exceeds 950° C., it becomes impossible toobtain the desired hardness due to surface decarbonization; and if, onthe other hand, the aforementioned temperature does not reach 800° C.,sufficient hardening cannot be attained, which is undesirable.

Furthermore, it is desirable to carry out oil-cooling after heatingduring the aforementioned high frequency hardening process. Ifwater-cooling is used with an high carbon Fe-sintered body like the onein the present invention, there is a high probability that quenchingcracks will occur.

The final low temperature tempering treatment is carried out (temperprocessing) to further increase the radial crushing strength constant ,and if the aforementioned temperature exceeds 220° C., the productsoftens and there is the inconvenience that the required hardness cannotbe attained.

PREFERRED EMBODIMENTS FOR IMPLEMENTING THE INVENTION

Next, an explanation is given on the best form for implementing thepresent invention.

First, the composition containing (weight %) C at 0.4-0.9%, Ni at1.5-4.0%, Mo at 0.2-0.6%, and a remainder of Fe and unavoidableimpurities is compacted to a density of 6.5-7.1 g/cm³ and morepreferably to a density of 6.7-7.0 g/cm³. Then, a primary sintering iscarried out on this for 20-40 minutes within a temperature range of1100°-1160° C.; re-heating is carried out subsequently within atemperature range of 900°-1100° C., and at the same time, forging iscarried out under an inert or reducing atmosphere so that the density isincreasing to a value over 7.7 g/cm³. Next, by carrying out a secondsintering for another 20-40 minutes within a temperature range of1100°-1160° C., under an atmosphere of RX, N2, AX etc., preferably underRX, the sintered body is obtained.

Then, after the hardening of the sintered body has been carried out byheating under a carbonizing atmosphere within a temperature range of800°-950° C. and by oil quenching, the high temperature tempering iscarried out for 20-60 minutes within a temperature range of 570°-700° C.under an inert or reducing atmosphere. Thereby the hardness of themiddle layer, which is more than 2,5 mm below the surface ofaforementioned sintered body, comes to lie within the aforementioned HCR25-40 range. In this way, the hardness at the middle layer does notbecome too high and a superior toughness is obtained. Next, hardening iscarried out at the surface layer of the inner periphery and/or outerperiphery which will be the sliding portions of the sintered body. It isdesirable that the hardening for this surface layer is carried out byoil-quenching after heating the sintered body at a temperature within arange of 800°-950° C., by high frequency heating. By the process ofhardening of this surface layer as above, the aforementioned surfacelayer is hardened to a depth of not more than 2.5 mm from the surface ofthe aforementioned sintered body, and a value within the range of HRC58-63, which is a hardness usually required for this type of slidingparts, is obtained.

Then, by carrying out low temperature tempering (temper processing)within a temperature range of 160°-220° C. on the aforementionedsintered body, a ring-shaped part with a further increased radialcrushing strength constant can be obtained.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a front view showing an example of a ring-shaped partmanufactured according to the present invention.

FIG. 2 is a cross section of the ring-shaped part shown in FIG. 1.

FIG. 3 is a graph showing the relation between the hardness of thesintered body and the temperature at which it was tempered.

FIG. 4 is a schematic block diagram showing an example of a highfrequency hardening apparatus.

FIG. 5 is a graph showing the radial crushing strength constant of apart manufactured according to the preferred embodiment of the presentinvention and of parts manufactured by comparative methods.

FIG. 6 is a graph showing the distribution conditions of the hardness indepth direction of the inner peripheral surface of the ring-shaped partaccording to the present invention.

FIGS. 7 and 8 are graphs showing the hardness distribution conditions inthe depth direction of the inner peripheral surface of the ring shapedpart, each manufactured by conventional methods.

PREFERRED EMBODIMENTS

Hereinafter, the inner periphery of an outer race of a one-way clutchserves as an example for a ring-shaped part, and the first preferredembodiment of the manufacturing method for ring-shaped parts in thisinvention is explained with reference to FIGS. 1-6. First, raw materialpowder (2% Ni, 0.5% Mo, 0.7% C, remainder Fe) is compacted by using amold to form a compacted body, a green compact. Then, after sinteringthis compact for 20 minutes at 1150° C., the sintered compact is forgedto a predetermined shape which then undergoes a second sintering for 30minutes at 1150° C. Then, processes such as cutting and grinding arecarried out on the sintered body and a ring-shaped sintered body L ofpredetermined dimensions (outer diameter: 134.65 φ, inner diameter: 105φ, thickness: 17 mm), as shown in FIG. 1 and FIG. 2, is produced.

Next, after having carried out hardening by heating the ring-shapedsintered body L at 850° C. and quenching it, the hardened item S istempered for 30 minutes at a high temperature to reach a hardness withina range of HRC 28-38.

FIG. 3 shows the relationship between hardness and temperingtemperature. As indicated in this figure, the hardness can be adjustedto HRC 28-38 by setting the tempering temperature to 570°-700° C.

Next, the surface layer of the inner periphery of the tempered hardeningproduct S, is hardened. This hardening is carried out by high frequencyhardening, whereby a high frequency hardening apparatus A, like the oneshown in FIG. 4, is used.

Here, explanations are given on the hardening apparatus A, and in thesame figure symbol 1 and 2 show the jigs which support hardened item S.Jig 1 is of an approximate cylindrical shape, and at the inner rim partof the top surface thereof, a counter bore part 3 is formed. On theother hand, aforementioned jig 2 has a hollow disk shape, and at theinner rim part of the lower surface thereof, a counter bore part 4 isformed. Jig 2 is provided so that it is freely separable from jig 1, andby making aforementioned jig 2 approach jig 1, the hardening item S isplaced on the counter bore part 3 of jig 1 is clamped by the counterbore part 4 to be held there. Furthermore, aforementioned jigs 1 and 2are set up to freely move up and down while holding the hardening item Sand further can rotate round its axis.

At the inner periphery of aforementioned jigs 1 and 2, a heating part 5is provided and separated from the hardening item S at a fixed distance.At the lower surface part of this heating part 5, a pair of upper andlower rectangular coils 6 is disposed so that they face towards theinner peripheral surface of hardening item S. Furthermore, these coilsare separated from one another at the lower end of the heating part 5, acooling part 7 is installed. At the outer periphery of this cooling part7, a large number of nozzles 8 is formed for spraying the cooling water,and when the hardening item S, which is high frequency hardened by coils6 of heating part 5, is lowered by jigs 1 and 2 and positioned at theouter periphery of the aforementioned cooling part 7, cooling water isblown from nozzles 8 against the inner peripheral surface of hardeneditem S.

Then, after having heated only the surface layer of the inner peripheryof hardening item S to a temperature of approximately 900° C. with thehigh frequency hardening apparatus of the aforementioned construction,by hardening and oil-quenching the hardness of the surface layer isincreased to a range within HRC 58-63 and the wear resistance of theaforementioned parts is increased .

With regard to FIG. 4, by changing the size of jigs 1 and 2, which holdhardening item S, (in this case, the high frequency conditions areconstant), the depth of the hardened layer can be regulated as shownhereinafter.

    ______________________________________                                                      depth of the                                                    Inner diameter                                                                              hardened layer                                                  of the jigs   of the surface (in mm)                                          ______________________________________                                        φ 110     1.5-1.8                                                         φ 112     2.0-2.3                                                         φ 114     2.5-2.7                                                         ______________________________________                                    

Besides, in this kind of high frequency hardening, cooling generallyproceeds fast at both end surfaces of hardened item S which contact theatmosphere, whereas in the center part, it is difficult for the heat todissipate, and therefore there is a tendency that the hardening depth atthe aforementioned both end surfaces and the center part becomesnon-uniform. Here, if the aforementioned high frequency hardeningequipment is used, it is possible to attain a heat-keeping effect at theparts of the aforementioned end surfaces by jig 1 and 2, which arelocated at both end surfaces of the hardening item S, and therefore therange of non-uniformity in depth direction of the hardened layers can besuppressed to be less than 1 mm.

Next, the hardened item S for which high frequency hardening has beencompleted is tempered (temper processing) at a relatively lowtemperature (approximately 180° C. for 30 minutes).

A compression load was applied in a direction orthogonal to the axisdirection of the ring-shaped part which underwent the aforementionedheating process, and the radial crushing strength constant measured wasapproximately 282 kg/mm², as shown in FIG. 5.

With regard to comparative examples 1-5, the ring-shaped parts underwentvarious heating processes described hereafter and a compression load wasapplied to each of them orthogonal to axis direction and the radialcrushing strength constant at the time of fracture was measured. Theresults are shown in FIG. 5. The dimensions of the comparativering-shaped parts were set equal to the dimensions of the ring-shapedparts in the present invention.

    ______________________________________                                        Comparative example 1                                                                       sintered body                                                   Comparative example 2                                                                       sintered body + carburizing hardening                           Comparative example 3                                                                       sintered body + high frequency                                                hardening + (low temperature)                                                 tempering process                                               Comparative example 4                                                                       sintered body + carburizing harden-                                           ing + high frequency hardening +                                              (low temperature) tempering process                             Comparative example 5                                                                       sintered body + carburizing harden-                                           ing + (high temperature) tempering                              Present Invention                                                                           sintered body + carburizing harden-                                           ing + (high temperature) tempering +                                          high frequency hardening + (low                                               temperature) tempering process                                  ______________________________________                                    

Here, the sintered body is one which follows the sintering of thecompacted powder body and forging to a predetermined shape, a secondsintering is performed and processes such as cutting and grinding arecarried out thereon to form the aforementioned ring shape which is theshape of the product.

As shown in FIG. 5, the ring-shaped part of the present invention hassuperior radial crushing strength constant in comparison to thering-shaped parts of comparative examples 1-5.

Furthermore, the distribution conditions of the hardness in the depthdirection of the ring-shaped part concerned in the present invention areshown in FIG. 6. As shown in this figure, the ring-shaped part possessesa surface layer hardness of approximately 60 HRC up to a depth of 2.0 mmfrom the surface and a hardness of a middle layer of approximately 38HRC for a depth exceeding 2.0 mm. As a result of this, according to theaforementioned ring-shaped part, the sliding portions possess a highhardness and superior abrasive resistance, the middle layer has asuitable hardness and superior toughness, and thereby achieving the highmechanical strength in the whole body, in other words, a high radialcrushing strength constant.

On the other hand, FIG. 7 and FIG. 8, respectively, show thedistribution conditions of the hardness in the depth direction of theinner peripheral layer of the ring-shaped part in the aforementionedcomparative examples 3 and 4. According to these figures, in comparativeexample 3, the hardness at a depth of 2.3 mm is 23 HRC and does not meetthe aforementioned requirements; whereas in comparative example 4, therequirements of hardness are met, however, the hardness at a depth whichexceeds the value 2.3 mm is to great at HRC 44-55 and the toughnesstherefore low; and as shown in FIG. 5, the radial crushing strengthconstant is also low.

High frequency hardening was carried out in order to increase thehardness of the surface layer of the inner periphery of the ring-shapedpart in the above preferred embodiment, however, carburization or otherhardening methods may be applied instead.

Possibilities for Industrial Applications

Since, in the manufacturing process of the ring-shaped part in thepresent invention, a high hardness required at the inner and outerperipheral surface was obtained and the toughness at the middle layer issuperior, and consequently ring-shaped parts which have a high radialcrushing strength constant as a whole can be easily obtained, there aremany industrial applications to make suitable use of it in themanufacturing of all kinds of ring-shaped mechanical parts havingcomplicatedly shaped sliding parts having protrusions and depressions atthe outer or inner surfaces, such as gears, pulleys, races of forwardone way clutches for the use in automatic transmission of automobiles,cams and sprockets, etc.

What is claimed is:
 1. A manufacturing method for ring-shaped parts,characterized in that a raw material powder composition comprising C at0.4-0.9% by weight, Ni at 1.5-4.0% by weight, Mo at 0.2-0.6% by weight,and a remainder consisting of Fe and unavoidable impurities, iscompacted; thereafter sintered and forged; then, after obtained sinteredbody is heated at a temperature within a range of 800°-950° C., hightemperature tempering is carried out for 20-60 minutes at a temperaturewithin a range of 570°-700° C., then the surface layers of the innerperiphery and/or the outer periphery of said sintered body is subjectedto hardening treatment.
 2. A manufacturing method for ring-shaped partsaccording to claim 1, characterized in that the hardening treatment ofthe surface layer of the sintered body is performed by heating within arange 800°-950° C., with the use of high frequency hardening, followedby oil-quenching.
 3. A manufacturing method for ring shaped partsaccording to one of claims 1 and 2, characterized in that aftercompacting and shaping said raw material powder, sintering is performedfor 20-40 minutes at a temperature within a range of 1100°-1160° C.,then, after having carried out forging, a second sintering is carriedout for 20-40 minutes at a temperature within a range of 1100°-1160° C.4. A manufacturing method for ring-shaped parts, characterized in that araw material powder composition comprising: C at 0.4-0.9% by weight, Niat 1.5-4.0% by weight, Mo at 0.2-0.6% by weight and a remainderconsisting of Fe and unavoidable impurities, is compacted and shaped;thereafter sintered and forged; and a sintered body obtained is hardenedat a temperature within a range of 800°-950° C., and then hightemperature tempering is carried out for 20-60 minutes at a temperaturewithin a range of 570°-700° C., then the surface layer of the innerperiphery and/or the outer periphery of said sintered body is processedby hardening, and then low temperature tempering (temper process) iscarried out at a temperature within a range of 160°-220° C.
 5. Amanufacturing method for ring-shaped parts according to claim 4,characterized in that the hardening of the surface layer of thesintered body is performed by heating within a range of 800°-950° C.with the use of high frequency hardening , followed by oil-quenching. 6.A manufacturing method for ring-shaped parts according to one of claims4 and 5, characterized in that after having compacted and shaped saidraw material powder, sintering is performed for 20-40 minutes at atemperature within a range of 1100°-1160° C.; then, after having carriedout forging, a second sintering is carried out for 20-40 minutes at atemperature within a range of 1100°-1160° C.
 7. A manufacturing methodfor ring-shaped parts according to claim 6, characterized in that saidforging is performed by reheating at a temperature within a range of900°-1100° C., and under an inert or a reducing atmosphere.